A metal-oxide-semiconductor (MOS) transistor is one of the most important components in modern integrated circuits. A MOS transistor usually includes: a semiconductor substrate, gate structures on the semiconductor substrate; and source/drain doped regions in the semiconductor substrate on sides of each gate structure. Each gate structure usually includes a gate dielectric layer on the semiconductor substrate and a gate electrode layer on the gate dielectric layer.
As semiconductor technologies continuously develop, a control ability of a conventional planar MOS transistor on channel currents becomes weaker, resulting in serious leakage current effects. A fin field effect transistors (FinFETs) is a kind of new multi-gate device. A FinFET usually includes: fins protruding from the semiconductor substrate; gate structures covering a part of top surfaces of the fins and a part of sidewalls of the fins; and source/drain doped regions in the fins on sides of each gate structure.
However, semiconductor devices made from the FinFETs have poor performances.